Problems Associated with Quality control Sampling in Modern IC Manufacturing

Existing sampling plans are not very efficient in situations when a fraction of defective items is on the order of 0.0001. They usually command a 100-percent inspection, but it still does not provide for 100percent quality since in semiconductor manufacturing the inspection is never totally reliable and can easily introduce an error of almost the same order as the fraction of defectives. Skip-lot strategies can rarely be used because most of the customers frequently require inspection of every shipped lot. An inspection policy is suggested which combines the ideas of various sampling strategies and provides a guarantee against undesirable levels of average outgoing quality as well as protection against poor quality on a lot-to-lot basis. The method is based on observing the number of good items between defective ones and shifting to a 100percent inspection when certain conditions are not met.